1. Field
The present invention is related to a method for producing metal castings with controlled grain size, a system for producing the metal castings, and products obtained by the metal castings.
2. Description of the Related Art
Considerable effort has been expended in the metallurgical field to develop techniques for casting molten metal into continuous metal rod or cast products. Both batch casting and continuous castings are well developed. There are a number of advantages of continuous casting over batch castings although both are prominently used in the industry.
In the continuous production of metal cast, molten metal passes from a holding furnace into a series of launders and into the mold of a casting wheel where it is cast into a metal bar. The solidified metal bar is removed from the casting wheel and directed into a rolling mill where it is rolled into continuous rod. Depending upon the intended end use of the metal rod product and alloy, the rod may be subjected to cooling during rolling or the rod may be cooled or quenched immediately upon exiting from the rolling mill to impart thereto the desired mechanical and physical properties. Techniques such as those described in U.S. Pat. No. 3,395,560 to Cofer et al. (the entire contents of which are incorporated herein by reference) have been used to continuously-process a metal rod or bar product.
U.S. Pat. No. 3,938,991 to Jackson et al. (the entire contents of which are incorporated herein by reference) shows that there has been a long recognized problem with casting of “pure” metal products. By “pure” metal castings, this term refers to a metal or a metal alloy formed of the primary metallic elements designed for a particular conductivity or tensile strength or ductility without inclusion of separate impurities added for the purpose of grain control.
Grain refining is a process by which the crystal size of the newly formed phase is reduced by either chemical or physical/mechanical means. Grain refiners are usually added into molten metal to significantly reduce the grain size of the solidified structure during the solidification process or the liquid to solid phase transition process.
Indeed, a WIPO Patent Application WO/2003/033750 to Boily et al. (the entire contents of which are incorporated herein by reference) describes the specific use of “grain refiners.” The '750 application describes in their background section that, in the aluminum industry, different grain refiners are generally incorporated in the aluminum to form a master alloy. A typical master alloys for use in aluminum casting comprise from 1 to 10% titanium and from 0.1 to 5% boron or carbon, the balance consisting essentially of aluminum or magnesium, with particles of TiB2 or TiC being dispersed throughout the matrix of aluminum. According to the '750 application, master alloys containing titanium and boron can be produced by dissolving the required quantities of titanium and boron in an aluminum melt. This is achieved by reacting molten aluminum with KBF4 and K2TiF6 at temperatures in excess of 800° C. These complex halide salts react quickly with molten aluminum and provide titanium and boron to the melt.
The '750 application also describes that, as of 2002, this technique was used to produce commercial master alloys by almost all grain refiner manufacturing companies. Grain refiners frequently referred to as nucleating agents are still used today. For example, one commercial suppliers of a TIBOR master alloy describes that the close control of the cast structure is a major requirement in the production of high quality aluminum alloy products.
Prior to this invention, grain refiners were recognized as the most effective way to provide a fine and uniform as-cast grain structure. The following references (all the contents of which are incorporated herein by reference) provide details of this background work:    Abramov, O. V., (1998), “High-Intensity Ultrasonics,” Gordon and Breach Science Publishers, Amsterdam, the Netherlands, pp. 523-552.    Alcoa, (2000), “New Process for Grain Refinement of Aluminum,” DOE Project Final Report, Contract No. DE-FC07-98ID13665, Sep. 22, 2000.    Cui, Y., Xu, C. L. and Han, Q., (2007), “Microstructure Improvement in Weld Metal Using Ultrasonic Vibrations, Advanced Engineering Materials,” v. 9, No. 3, pp. 161-163.    Eskin, G. I., (1998), “Ultrasonic Treatment of Light Alloy Melts,” Gordon and Breach Science Publishers, Amsterdam, The Netherlands.    Eskin, G. I. (2002) “Effect of Ultrasonic Cavitation Treatment of the Melt on the Microstructure Evolution during Solidification of Aluminum Alloy Ingots,” Zeitschrift Fur Metallkunde/Materials Research and Advanced Techniques, v. 93, n.6, June, 2002, pp. 502-507.    Greer, A. L., (2004), “Grain Refinement of Aluminum Alloys,” in Chu, M. G., Granger, D. A., and Han, Q., (eds.), “Solidification of Aluminum Alloys,” Proceedings of a Symposium Sponsored by TMS (The Minerals, Metals & Materials Society), TMS, Warrendale, Pa. 15086-7528, pp. 131-145.    Han, Q., (2007), The Use of Power Ultrasound for Material Processing,” Han, Q., Ludtka, G., and Zhai, Q., (eds), (2007), “Materials Processing under the Influence of External Fields,” Proceedings of a Symposium Sponsored by TMS (The Minerals, Metals & Materials Society), TMS, Warrendale, Pa. 15086-7528, pp. 97-106.    Jackson, K. A., Hunt, I. D., and Uhlmann, D. R., and Seward, T. P., (1966), “On Origin of Equiaxed Zone in Castings,” Trans. Metall. Soc. AIME, v. 236, pp. 149-158.    Jian, X., Xu, H., Meek, T. T., and Tian, Q., (2005), “Effect of Power Ultrasound on Solidification of Aluminum A356 Alloy,” Materials Letters, v. 59, no. 2-3, pp. 190-193.    Keles, O. and Dundar, M., (2007). “Aluminum Foil: Its Typical Quality Problems and Their Causes,” Journal of Materials Processing Technology, v. 186, pp. 125-137.    Liu, C., Pan, Y, and Aoyama, S., (1998), Proceedings of the 5th International Conference on Semi-Solid Processing of Alloys and Composites, Eds.: Bhasin, A. K., Moore, J. J., Young, K. P., and Madison, S., Colorado School of Mines, Golden, Colo., pp. 439-447.    Megy, J., (1999), “Molten Metal Treatment,” U.S. Pat. No. 5,935,295, August, 1999    Megy, J., Granger, D. A., Sigworth, G. K., and Durst, C. R., (2000), “Effectiveness of In-Situ Aluminum Grain Refining Process,” Light Metals, pp. 1-6.    Cui et al., “Microstructure Improvement in Weld Metal Using Ultrasonic Vibrations,” Advanced Engineering Materials, 2007, vol. 9, no. 3, pp. 161-163.    Han et al., “Grain Refining of Pure Aluminum,” Light Metals 2012, pp. 967-971.